Composite piston



March 3, 1931. N. A. BEST ET AL 1,794,827

COMPOSITE PISTON Filed Jan. 14, 1926 I N V EN TORJ Patented Mar. 3, 1931 UNITED STATES PATENT OFFICE NORMAN A. BEST AND JOHN E. HOY, OF MIDLAND, MICHIGAN, ASSIGNORS TO THE DOW CHEMICAL COMPANY, 01E MIDLAND, MICHIGAN, A CORPORATION OF MICH- IGAN oomrosrrn rrs'ron Application filed January 14, 1926. Serial No. 81,241.

iron or of steel, we have heretofore designed a piston of composite structure that forms the subject-matter of our co-pending application filed March 18, 1924, Ser. No. 699,978 (Patent No. 1,570,837). This improved piston is characterized, among other things, by

having a cylindrical body composed of a light metal alloy and a shell surrounding said body and composed of a ferrous metal, said shell being formed with a series of circumferen-.

tially spaced openings wherein projections from said body extend.

In commei chi and other tests made of the design of piston'in question, we have found that while such surrounding shell, if of sulficiently substantial construction, serves to restrain undue expansion on the part of the skirt portion of the piston contained therein, the projections from such skirt nevertheless tend, when the piston is subjected to the high temperature of operation in an internal combustion engine, to expand sufficiently to cause their outer ends to project beyond the circumjacent surface of said shell and to a corresponding extent neutralize the result which it is desired to obtain. The objectofthepresent invention, accordingly, is to overcome this difficulty and to this end the invention, then, consists of the means hereinafter fully described and particularly pointed out in the claims, the annexed drawing and the following description setting forth in detail certain mechanism embodying the invention, such disclosed means constituting, however, but several of the various ways in which the principle of the invention may be used.

In said annexed drawing Fig. 1 is partly a side elevation and partly a central vertical section of a piston embodying our present improvements; Fig. 2 is a central vertical section of such piston, the plane thereof being at right angles to the plane of the sectioned portlon of Fig. 1; and Figs. 3 and 4 are respectively an elevation and section of a detail of such piston having a slightly modified construction.

In its general features the present improved piston is similar to the one described in our above identified co-pending application. In other words, the body of such piston, which is composed of a light metal alloy, for example one of the numerous magnesium base alloys available for the purpose, com- I prises a more or less cylindrical head portion 1, from which depends a sleeve or skirt portion 2. Such sleeve or skirt portion is formed with oppositely placed inwardly directed bosses 3 which are apertured to receive the wrist pin (not shown) whereby the piston is attached to the connecting rod. Bushings 4 of bronze or equivalent bearing metal are preferably fitted to the apertures in such bosses, as best shown in Fig. 1, and an integral rib 5 between each boss and the head 1 contributes to the strength of the structure. In order efit'ectually to seal the piston within the walls of the cylinder in which it works, resilient piston rings (not shown), of familiar construction, are seated in annular recesses 6 in the head portion 1 as need not be further explained.

Referring to the specific form of our improved piston illustrated in Figs. 1 and 2, it will 'be seen that the skirt portion 2 is substantially surrounded by a shell or band 7. In contradistinction to the light metal alloy whereof the piston proper is composed, as stated above, this shell or band will be made of either cast iron or steel or other metal of relatively low coefiicient of expansion that will correspond more nearly to the coefficient of expansion of the metal whereof the engine cylinder is composed. Where such shell, as in the construction illustrated in Figs. 1 and2, extends above the wrist pin openings in bosses 3, it will be formed with'corresponding openings 8, preferably of somewhat larger diameter, and the lower edge of such shell will furthermore terminate somewhat ing with integral projecting portions 10 of the piston skirt.

It will be understood that the metal c0m posing the piston proper (head 1 and skirt 2) is cast in a suitable mold in which such shell or band 7 has been previously placed, the walls of the mold being formed to give the proper contour to the exposed portions of the body and skirt. Such exposed portions, as just indicated, will include the projections 10 on the skirt, as also the lower edge of the latter which projects in -the form of a flange 11, adjacent the lower edge of the shell, and a semi-circular flange 12 that lies Within each wrist pin opening 8 in the shell. The feature of construction to which the aforesaid application is directed is the inclination of the laterally contacting surfaces of the lower edge of the shell and of the edges of openings 8 and 9 therein with the opposed surfaces-of flanges 11 and 12 and the projections 10 on the skirt of the piston and this feature, accordingly, need not be further referred to in the present connection. Instead, however, of leavingsuch flanges 11 and 12 and projections 10 flush with the outer cylindrical surface of the shell, we have found that a superior operative effect is obtained if they be turned or otherwise machined back so as to stop short of the circumjacent outer surface of the shell at normal temperature. The flange 11 may be readily thus turned down so as to have a slightly smaller diameter than the lower edge of the shell, while as affording the most convenient way to relieve the ends of the projections 10, we turn a shallow circumferential groove 15 coincident with each series of such projections and of a width approximately equal to the diameter of the openings 9. The flange 12 is similarly planed or turned back so as to be relieved, i. e. lie at normal temperature within tge 1elxdge of the surrounding opening 8 in said s e If desired, instead of turning such relief groove 15 in the shell coincident with the several series of projections 10, each of the latter, as shown in Figs. 3 and 4, may be sepa rately cut back or relieved in order to prevent them from binding on the cylinder wall when the skirt portion of the light metal piston body expands. The depth of the recesses 16 thus left in the shell at normal temperature will be the same as that of the grooves 15, such depth in each case being sufiicient to allow the projections or buttons of light metal alloy to expand to their maximum extent without their ends coming-into bearing contact with the cylinder bore. Such shallow groove has furthermore the functional advantage of serving to collect the lubricant introduced between the piston and cylinder bore and thus assist in spreading such lubricant in operation.

Other modes of applying theprinciple of our invention may be employed instead of the one explained, change being made as regards the mechanism herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

We therefore particularly point out and distinctly claim as our invention 1. In a piston or like article, the combina tion with a body composed of a metal having a relatively high coeflicient of expansion; of a shell surrounding and covering a substantial portion of the surface of said body in circumferential direction and seated throughout in intimate contact therewith and composed of a metal having a relatively low cocflicicnt of expansion, said shell being formed with openings wherein projections from said body extend, the outer surfaces of said shell being formed with a shallow encircling.

groove coincident with suchopenings, and the outer ends of said projections at normal temperature lying approximately flush with the body of such groove.

2. In a piston or like article, the combination with a body composed of a light metal alloy; of a shell of ferrous metal surrounding and covering a substantial portion of the surface of said body uninterruptedly in a circumferential direction and seated in intimate contact therewith, said shell being formed with a series of circumferentially spaced openings wherein projections from said body extend, the outer surface of said shell being formed with a shallow, encircling groove coincident with such openings and the outer ends of said projections at normal temperature lying approximately flush with the bottom of such groove.

Signed by us, this 8th day of January, 1926..

NORMAN A. BEST. JOHN E. HOY.' 

